This invention concerns an assembly for permitting “Power-over-Ethernet” (PoE) (also sometimes referred to as “power over LAN”) connection.
PoE is a subject of rapidly growing interest at the present time. The technology involves the provision of electrical power using Ethernet cabling such as that defining a local area network (LAN).
A typical “Category 5” data transmission cable (which is a type very commonly used in LAN cabling applications) consists of four twisted pairs of conductor wire. These are used to transmit data in the form of voltages whose maximum and minimum values are dictated by internationally agreed standards.
It is possible to use data cables of this kind for the provision of electrical power as well as data, without reducing the ability of the cables simultaneously to transmit data reliably and without crosstalk.
This is achieved primarily through the use of both active control elements and certain passive components (such as centre-tapped secondary windings of transformers forming part of the LAN) that permit the connection of power supplies to the data cables. The active and passive components limit the voltages transmitted via the cables so that they lie within the maximum and minimum values permitted under the aforesaid standards.
In some applications of PoE technology the transmission of data and electrical power occurs simultaneously using the same pairs of the cables. In other applications there is a mix of uses such that some of the pairs are used for mixed data and power transmission and others are dedicated to the transmission of either power or data.
Various devices are capable of operating at the power levels provided using PoE technology. Such devices if connected to the node of a LAN may draw operating power from the network without any need for a separate connection to mains power. Such devices include internet protocol (JP) telephones, charge-coupled device (CCD) cameras, sensors of alarm systems, card readers and similar apparatuses. There is even available a personal computer that operates at the power levels available from a PoE arrangement.
Also a PoE-enabled network may provide backup power to devices, such as conventional personal computers, at times when mains power is unavailable. In such applications the active devices controlling the distribution of power over the LAN in question can be arranged to send network messages to devices connected at its nodes, thereby initiating modes of operation that minimise power consumption.
The advantages of providing power over a LAN or Ethernet are such that interest in this technology is growing rapidly. However, many buildings and other locations where network cabling is installed do not incorporate the active and passive components needed to permit the transmission of power.
The structured (i.e. built-in) cabling of a new building is nowadays intended to remain in use for 10-20 years. Therefore in the majority of applications it would be uneconomical to replace it with cabling incorporating the parts needed to provide Power over Ethernet transmission.
It is desirable to be able to upgrade the electronic components needed on a more frequent basis than the 10-20 year life of structured LAN cabling.